The present invention relates to a novel unsymmetrical dioxazine compound that can be used as a dichroic dye useful in the art of liquid crystal display elements, a dichroic dye, a liquid crystal composition, and a liquid crystal display element fabricated with the liquid crystal composition.
Compositions containing a liquid-crystalline material and a small amount of a dichroic dye are used for production of liquid crystal display elements of a guest-host type (abbreviated as GH hereinbelow). The GH system is an important system of liquid crystal display elements. This system, which utilizes the colors of dichroic dyes to realize colored display, has recently been attracting attention as means for improving the efficiency of light utilization in color liquid crystal display elements, without requiring color filters. A variety of GH liquid crystal display elements have been drawing interests, such as those consisting of a laminate of Heilmeier type GH cells, those consisting of a laminate of double layer GH type liquid crystal display elements (DGH), and those consisting of a laminate of cholesteric-nematic phase change GH type liquid crystal display elements (PCGH) Recently, reflection type liquid crystal display elements are of particular interest in view of energy conservation or securance of battery life in portable devices. The reflection type liquid crystal display elements lack auxiliary light sources such as back lights, so that use of such GH liquid crystal display elements in the reflection type elements is believed to be advantageous due to their high efficiency of light utilization.
As dichroic dyes for the GH liquid crystal displays, excellent materials with high dichroic ratios have been developed, such as azo dyes, anthraquinone dyes, and quinophthalone dyes. Such materials exhibit high dichroic ratios in many liquid-crystalline materials (Alexander V. Ivashchenko, Dichroic Dyes for Liquid Crystal Displays, p165-337, (CRC Press), 1994).
In general, the absorption spectra of dichroic dyes have considerable influence on colored display of GH liquidcrystaldisplays. Thus, inordertobroadenthe range of the displayable color tones and to ensure color rendering properties, it is necessary to control each of the primaries independently and to combine dyes which overlap little in absorbable wavelength.
The overlap of absorbable wavelengths prevents the independent control of the primaries to narrow the range of the displayable colors, and accompanies additional light absorption to lower the efficiency of light utilization. For avoiding the overlap of absorbable wavelengths, selection of the peak absorption wavelength for each color is important. However, mere selection of the peak absorption wavelength still allows some overlap of absorbable wavelengths since absorption spectra of dyes are generally broad. Thus, it is particularly advantageous for dichroic dyes to have as narrow light absorption bands as possible in order to reduce the overlap.
Dioxazine dyes were originally developed as a kind of pigments, and are now generally known to have a narrow light absorption band and to exhibit vivid color tones.
However, the dichroic ratios of conventional dichroic dyes having a dioxazine skeleton are relatively low in liquid crystal, i.e. about 6 to 7, compared to those of azo dyes and anthraquinone dyes (Alexander V. Ivashchenko, Dichroic Dyes for Liquid Crystal Displays, p173, (CRC Press), 1994). Consequently, development of dioxazine dyes with higher dichroic ratios is desired.
It is an object of the present invention to provide a novel unsymmetrical dioxazine compound having a narrow light absorption band and a high dichroic ratio, a dichroic dye, a liquid crystal composition, and a liquid crystal display element fabricated with the same.
The present inventors have made intensive studies for achieving the above object to find out that a novel compound having an unsymmetrical dioxazine skeleton with particular substituents incorporated thereto has a high dichroic ratio in liquid crystal, thereby completing the present invention.
According to the present invention, there is provided an unsymmetrical dioxazine compound represented by the formula (1-1) or (1-2): 
wherein each of Y1 to Y3 stands for a group represented by the formula (2) or (3) with at least one of Y1 to Y3 being a group represented by the formula (2); X stands for a hydrogen atom, a halogen atom, a cyano group, an alkyl group, an aryl group, an alkoxy group, an acylamino group, or a carboxylate group: 
wherein h is an integer of 0 to 2, i is an integer of 1 to 2, and j is an integer of 0 to 2; A stands for a group selected from group (I) consisting of: 
wherein k is an integer of 1 to 6; one or more of hydrogen atoms in a phenylene group may be substituted by an alkyl group having 1 to 12 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, a perfluoroalkyl group having 1 to 6 carbon atoms, or a halogen atom; when A is a group having ends (a) and (b), the end (a) binds to E or G and the end (b) binds to the ester group in the formula (2);
each of E, J, and M stands for a group selected from group (II) consisting of: 
wherein m is an integer of 1 to 12, and each of q and r is an integer of 1 to 8; one or more of hydrogen atoms in a phenylene group may be substituted by an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a perfluoroalkyl group having 1 to 6 carbon atoms, or a halogen atom; when E in the formula (2) is a group having ends (a) and (b) , the end (a) binds to G or E and the end (b) binds to A or E; when J in the formula (3) is a group having ends (a) and (b) , the end (a) binds to M, J, or Q, and the end (b) binds to J or a triphenodioxazine skeleton; when M in the formula (3) is a group having ends (a) and (b) the end (a) binds to M or Q and the end (b) binds to M or J;
G and Q each stands for a group selected from group (III) consisting of: 
wherein n is an integer of 1 to 12, and each of q, r, and s is an integer of 1 to 8.
According to the present invention, there is also provided a dichroic dye consisting of an unsymmetrical dioxazine compound represented by the formula (1-1) or (1-2).
According to the present invention, there is also provided a liquid crystal composition comprising at least one dichroic dye mentioned above and a liquid-crystalline material.
According to the present invention, there is also provided a liquid crystal display element comprising at least one liquid crystal composition mentioned above as a liquid-crystalline material.